In my opinion, the man is drinking water. If you look closely at the maze of tubes, you can see that the tube connected to the bottle he is holding ultimately leads to the cup marked “WATER.” Although the tubes appear very complicated and cross each other several times, the correct path starts at the bottle and follows the curves down to the cup of water.
Other drinks like tea, coffee, and juice also have tubes, but when you follow their paths, you'll notice that they're not directly connected to the bottle the person is drinking from. Some tubes cross each other or appear to be connected, but in reality, they don't lead to the mouth.
